Photovoltaic cells are widely used to convert sunlight into electricity and are often interconnected with other photovoltaic cells in photovoltaic modules. Individual photovoltaic modules are usually encapsulated to protect the module components including the photovoltaic cells from the environment. Photovoltaic modules are traditionally mounted outdoors on rooftops or in wide-open spaces where their exposure to sunlight is maximized. When the intensity of sunlight increases, electrical output from photovoltaic modules also increases. However, the efficiency with which a photovoltaic module converts sunlight into electricity is usually only about 20%. The remaining about 80% of the sunlight is reflected back or absorbed by the module. Energy that is absorbed results in an increase of the operating temperature of the module. Excessive heat decreases the efficiency with which a photovoltaic module converts sunlight into electricity. The optimal operating temperature for most photovoltaic modules is around 47° C. Many photovoltaic modules lose about 0.5% efficiency for every degree Celsius that their operating temperature increases. A variety of factors may contribute to an increased operating temperature, such as greater ambient air temperature during the day, radiant heat from ground surfaces and other nearby surfaces which may emit heat generated from sun exposure, and increased temperature of the solar module itself from extended sun exposure.
This problem is often exacerbated in situations where photovoltaic modules are integrated in building structures which often have dark, for example black, backsheets for esthetic reasons. Usually, photovoltaic modules have backsheets that provide electrical insulation of the photovoltaic cells within the modules and protect the photovoltaic cells from the ingress of moisture and other environmental factors. While the typically rectangular photovoltaic cells in a photovoltaic module are located in close proximity, there are usually small gaps between them that expose the underlying backsheet to sunlight. In 10-15% of the total area covered by a typical mono crystal silicon photovoltaic module comprising 72 cells, the backsheet is exposed to direct sunlight. Where photovoltaic modules are integrated in a building structure, their backsheets are usually dark, for example black, to make the photovoltaic modules blend in with the existing architectural colors. The dark, or even black, appearance of the backsheet is usually generated by coating the backsheet with the pigment carbon black or iron oxide, or by mixing these pigments with the material the backsheet is made of during the process of manufacturing the backsheet. Carbon black absorbs basically all light visible to humans. In addition, carbon black also adsorbs infrared light, which is electromagnetic radiation with wavelengths longer than that of light generally visible to humans, i.e., with wavelengths ranging from the edge of visible red light at about 750 nm to about 300 μm. This absorption of infrared light increases the temperature of the backsheet and, ultimately, the operating temperature of the entire photovoltaic module. By contrast to black pigments like carbon black, pigments appearing completely white, for example, reflect most, and thus do no absorb any, light visible to humans, and they also reflect most of the infrared light. Thus, while dark, or even black, backsheets in photovoltaic modules are desirable for esthetic reasons, such backsheets tend to increase the photovoltaic modules' operating temperature. This reduces the photovoltaic modules' efficiency in converting sun light into electricity.
There remains a need for improved methods of optimizing the operating temperature of building-integrated photovoltaic modules. The present invention addresses this need.